Final answer:
Acetyl-CoA is the starting point for ketone body synthesis, specifically in the liver when the citric acid cycle is saturated and cannot process all the Acetyl-CoA produced from fatty acid oxidation.
Step-by-step explanation:
The starting point for ketone body synthesis is Acetyl-CoA. The process begins when Acetyl-CoA, which can be derived from fatty acid oxidation, is used in the liver for energy production through the citric acid cycle. When the citric acid cycle is overwhelmed due to an excess of Acetyl-CoA, the surplus is directed toward the production of ketone bodies through a process known as ketogenesis. This involves the conversion of Acetyl-CoA into acetoacetate, which can then be reduced to ß-hydroxybutyrate, or be decarboxylated to form acetone, another type of ketone body.